World War I lasted from 1914 to 1918. It was known at first as the Great War and the War to End All Wars. It was the largest war that the world had seen up to that time. Most of the battles took place in Europe and the Middle East. More than 8 million soldiers and sailors died, and more than 20 million were injured. The war was so bad that many people thought no one would ever start another war. However, the results of World War I helped to cause World War II, which broke out in 1939.

A murder in the city of Sarajevo led to the war. Sarajevo was the capital of Bosnia, a region of the Austro-Hungarian Empire. For many years, Austria-Hungary and its neighbor Serbia had been unfriendly. Serbian patriots wanted all Serbs to unite. They wanted Serbs living in Bosnia to break free of Austro-Hungarian control. On June 28, 1914, a Bosnian Serb shot and killed the Austro-Hungarian emperor’s nephew, Archduke Francis Ferdinand. Austria-Hungary accused Serbia of planning the crime.

On July 28 Austria-Hungary declared war on Serbia. Both countries asked for help from their friends. Austria-Hungary’s friends were Germany and Italy. Their group was called the Triple Alliance. Serbia was a small country, but Russia protected it. Russia’s friends were France and the United Kingdom (Great Britain). Their group was called the Triple Entente.

Within a few weeks most of the countries of Europe were at war. Both sides soon got new names. The Triple Alliance became the Central Powers, and the Triple Entente became the Allies. Italy did not go to war at first.

Battlefields west of Germany were called the Western Front. The Germans had hoped for an easy victory on the Western Front. But in September 1914 the Allies forced back the Germans at the First Battle of the Marne, near the Marne River in France.

The armies on the Western Front then began four years of trench warfare. Each side dug long trenches into the ground. The trenches stretched from the coast of Belgium to the border of Switzerland. The soldiers stayed in these trenches for protection. A “no-man’s land” covered with barbed wire lay between the trenches. Both sides used rapid-firing machine guns against anyone who tried to get across the no-man’s land.

Soldiers fought two of the war’s worst battles on the Western Front in 1916. The First Battle of the Somme took place near the Somme River in France from July to November. More than 600,000 soldiers on each side were killed, wounded, or captured. They gained only about 5 miles (8 kilometers) of ground. The French and the Germans fought another long battle near the French town of Verdun in 1916.

Both sides tried new ways to break through trench defenses. In April 1915, at the Second Battle of Ypres, the Germans used a poison gas called chlorine against Allied troops. Both sides then tried other chemical weapons. Soldiers got gas masks for protection against them. The British invented an armored car called a tank. Tanks used crawler tracks to move themselves through trenches and barbed wire. The British first used tanks in 1916 at the First Battle of the Somme.

Battlefields east of Germany were called the Eastern Front. Armies moved faster on the Eastern Front. In 1914 Russian armies pushed west into Germany and Austria-Hungary. The Germans responded to the Russian advance with a crushing blow at the Battle of Tannenberg in August 1914. Bulgaria then joined the Central Powers. The troops of Germany, Austria, and Bulgaria took Serbia. An Allied force landed at Salonika (now Thessaloníki) in Greece to help the Serbs. However, the Allies made little progress until the end of the war.

At the end of 1914 the Ottoman Empire (centered in what is now Turkey) joined the Central Powers. The Ottomans attacked Russia. Allied troops from Britain, Australia, and New Zealand tried to stop the Ottomans on Turkey’s Gallipoli Peninsula, but they failed.

In 1915 Italy joined the Allies. The Italians lost many soldiers fighting the Austrians.

When the war began, the Ottoman Empire ruled Syria, Palestine, and Mesopotamia (now Iraq). In 1915 British-led troops tried and failed to take Baghdad (now the capital of Iraq). In March 1917 they finally succeeded. Later that year, the British took Palestine. In 1918 they took Syria as well.

The British had more and better warships than the Germans. The British Navy was able to stop some ships from reaching German ports. Such an action is called a naval blockade.

However, the British were not able to stop German submarines, which were called U-boats. In 1915 the Germans announced that they would try to sink all enemy ships in British waters. On May 7, 1915, a German submarine sank the British passenger ship Lusitania. Nearly 1,200 people died, including many U.S. citizens.

The submarine attacks hurt the United Kingdom. By April 1917, one of every four supply ships that left the country never returned. By the end of that month, the United Kingdom had only a six-week supply of grain left.

The Allies tried to defend their supply ships by putting guns on them. They also had them sail in convoys, or groups, protected by warships. In all, German submarines caused the loss of about 6,000 Allied ships. The United Kingdom alone lost 13,000 lives in these attacks.

The airplane had been invented only 11 years before the war began. At first Germany used floating aircraft called zeppelins, rather than airplanes, to bomb the United Kingdom. Then the British built antiaircraft guns to shoot down the zeppelins.

During the war both sides built several kinds of warplanes. Fighter airplanes had machine guns to shoot at other airplanes. In 1917 the Germans started dropping bombs from airplanes. Large German planes bombed London and other cities. In the United Kingdom these bombings killed about 1,300 people and injured about 3,000.

The Russian Revolution in 1917 changed the Eastern Front. A group called the Bolsheviks took over Russia in November. They made peace with the Central Powers almost immediately. The Germans were then able to move their troops elsewhere.

Meanwhile, the United States entered the war on the side of the Allies. President Woodrow Wilson at first did not want to go to war. He changed his mind because Germany kept attacking U.S. supply ships. The United States also found out that Germany had promised to give Texas, New Mexico, and Arizona to Mexico in return for Mexico’s help in the war. The United States declared war on Germany on April 6, 1917.

During the winter of 1917–18, there were more German soldiers than Allied soldiers on the Western Front. In 1918 the situation changed, as nearly 10,000 U.S. troops landed each day in France. The Germans knew that the Americans were building up forces. They staged several attacks against the British and French to weaken them before the Americans arrived in force. The Germans had some success at the Second Battle of the Somme. However, the German troops were worn out. After the Second Battle of the Marne, in July 1918, the Allies had taken control of the war. By November, they had driven back the Germans to the battle lines of 1914.

The Central Powers started surrendering. The Bulgarians gave up on September 29, 1918. On October 30 the Austrians asked for a cease-fire (an end to fighting). The Ottomans gave up on the same day.

By this time, the German people were starving. The naval blockade was keeping food shipments from reaching the country. On November 11, 1918, German government leaders signed an armistice—an agreement that ended the fighting.

In January 1919 the leaders of the Allies met in Paris, France, to create a peace treaty. The treaty allowed Germany to keep only a small army and navy. Germany was also forced to pay a large amount of money to the Allies. In addition, the treaty started the League of Nations, an organization that was supposed to prevent future wars.

German and Allied representatives signed the Treaty of Versailles on June 28, 1919. (Versailles is a town near Paris.) The Allies later signed separate treaties with Austria, Bulgaria, and the Ottoman Empire. However, the U.S. Senate refused to ratify, or agree to, the Treaty of Versailles. Some senators were against the treaty because they did not like the League of Nations.

The Allies’ dreams of peace did not last long. The German people did not like being punished. They brought Adolf Hitler to power in 1933. He built up the German military. The League of Nations could not stop him. His actions eventually led to World War II.

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